The present invention relates to an approach that detects plated through hole voids in printed circuit boards using a pH-sensitive component included in the laminate of the circuit board or in an acid or base to which the an indicator bonds.
Plated through hole voids are a known issue when manufacturing printed circuit boards (PCB). Plated through hole voids may potentially cause failure during assembly and are also considered as a long term reliability issue of the printed circuit boards. Current understanding of the phenomenon indicates that the voids typically form during composite copper plating before external circuitization. For example, voids may form if the copper plating solution was blocked by air bubbles, foreign material, or dry film resist residues. During that period, the entire PCB is virtually encased in copper. The only areas where laminate would be exposed is at a defect site where there is a void in the copper. This defect is difficult to detect using currently-available inspection capability or test equipment. The voids may not entirely encircle the hole wall and thus may not result in an electrical open thereby making it difficult to detect by an electrical method. In the subsequent card assembly and field application processes, these voids may become an intermittent open, or even a dead open, due to high thermal stress in the assembly process or temperature cycling during the application stage.